What is the fuel-oil mix ratio on a 2004model cr250?

This would depend on what type of oil you will be using for your premix. The oil base stock is either petroleum, semi-synthetic or synthetic oil and is mixed with gas at a ratio ranging from 16:1 (petroleum) to as high as 100:1 (synthetic). I personally ride a 2001 Kawasaki KDX200 that I run Yamalube 2R at 36:1 with no problems. Although synthetics say you can mix them at 100:1 I would not, that seems way too lean to me. i use a 40:1 mix in my rm but i use a suzuki highgrade oil so naturally the better quality oil you use the leaner you can go but unless you like rebuilding top ends dont go leaner then 40:1. DONT USE CHEAP OIL . WITH A CHEAP CRAPPY BRAND YOU WILL HAVE TO RUN IT ON A RICHER MIX LIKE 32:1 BUT THIS WILL CAUSE THE SPARK PLUG TO FOWL VERY QUICKLY AND EVEN THOUGH THE MIX IS RICHER THAN A HIGH GRADE 40:1 MIX IT WONT BURN AND LUBRICATE NEARLY AS WELL AS THE HIGHRADE STUFF.